1. Field of the Invention
The present invention relates to a digital PWM generator and an apparatus for driving a light emitting device that can be applied to a light emitting diode (LED), a backlight unit (BLU), or the like, and precisely controlled.
2. Description of the Related Art
In general, a light emitting element such as an LED or the like can use a pulse width modulation (PWM) driving circuit in order to control the luminance thereof. Herein, a PWM scheme can control a current flowing in the light emitting element by controlling a high section within one cycle of a PWM control signal to 0 to 100%.
As described above, in a known LED driving apparatus using the PWM scheme, as a percentage of an on section within one cycle of a PWM signal increases, optical brightness within the LED increases.
That is, the PWM signal having a duty ratio controlled to have a desired luminance is generated and provided to a switching element so as to control the optical brightness of the LED.
For such an operation, the LED driving apparatus includes a driving circuit controlling the current flowing in the LED and a PWM signal generator generating the PWM signal having a duty ratio suitable for a desired luminance in order to drive the LED.
However, the known PWM driving circuit has the following defects when the known PWM driving circuit has the PWM signal generator included therein.
That is, in the case of a known internal PWM scheme, when a phase locked loop (PLL) is not used for miniaturization and low cost, a clock frequency is not accurately locked, and as a result, a waterfall phenomenon in which a stripe flows down on a screen occurs.
Further, when the phase locked loop (PLL) is used in order to remove the waterfall phenomenon, the waterfall phenomenon can be enhanced, but since the PLL has its own frequency offset due to the use of the PLL for accurate frequency locking, a frequency offset is generated between a clock of a system and the PWM signal.
Furthermore, fine duty control may be limited due to a constraint such as an offset or a response speed of a comparator used to generate the PWM signal.